For San Siro, read San Zero. Prior to this weekend, Milan and Internazionale had played a combined seven competitive fixtures this season at their shared stadium. Neither of them had come away from any of those games with a victory.

The scapegoat was all too obvious. For more than two decades – ever since a third tier was added to the stadium in preparation for the 1990 World Cup – the two clubs had struggled to maintain the pitch at San Siro, where insufficient sunlight made it impossible for grass to bed in. This summer, in a bid to resolve their issues once and for all, they had agreed to install a partially synthetic playing surface.

It was a decision several years in the making, but one that made practical sense. The two clubs had been paying to re-lay the pitch up to six times a season at a cost of almost €200,000 (£160,000) a time, whereas the artificial pitch could do away with all that for a one-off fee nearer to €750,000. There were hopes that more stable playing surface, too, might reduce injuries over the course of a campaign.

The early signs had been encouraging. "The grass at San Siro has already won" declared a headline in La Repubblica on 18 September – with the accompanying article noting that a first intervention had been already required on the pitch by the middle of the same month in 2011. This year the surface had shown no signs of cutting up despite Inter's early August start in the Europa League.

Sadly the results obtained on it were less positive. In their first Europa League qualifier, Inter almost blew a 3-0 lead from the away leg – losing 2-0 at San Siro. They would subsequently draw 2-2 with each of Vaslui and Rubin Kazan at home, and were beaten 3-1 by Roma in the league in-between. Milan lost their first two home games of a Serie A season for the first time in more than 80 years. They also drew 0-0 with Anderlecht in the Champions League.

Match reports began to make reference to maledizione – the notion that the pitch might be cursed. One or two bloggers even began to call in earnest for the archbishop of Milan to perform a blessing to cleanse it of dark energies.

Others, though, could see a more pragmatic solution. The simplest way to dismiss any 'curse' would be a match against a soft opponent. Thankfully the fixture list offered just such an opportunity to Inter on Sunday, with the visit of Serse Cosmi's Siena. The Robur had not won any of their first three games of the season, and with a wage bill roughly one-fifth the size of Inter's should have made for easy pickings.

Inevitably, they didn't. Aligned by Cosmi in a bold 3-4-2-1, Siena did not sit back and invite Inter on to them, but instead matched their hosts from the outset by pressing high up the pitch and setting the tempo. Although Inter still enjoyed the better of the first-half exchanges, they created little by way of real chances – Diego Milito became isolated, and Wesley Sneijder resorted quickly to potshots from outside the area.

Siena's goalkeeper, Gianluca Pegolo, made some sharp saves but was not overworked. As the game became stretched in the second half, so they sensed their moment. Twice they punctured Inter with rapid counter-attacks — first Simone Vergassola drove into the far corner after a neat exchange with Alessandro Rosina and Emanuele Calaiú on the edge of the area, then Francesco Valiani headed home an Alessio Sestu cross from close range in injury time.

Inter had no response. Optimistic reporters had noted in the buildup to the game that the last time Inter had failed to win any of their first four home games was 1970-71, a season in which they went on to win the league. But never, before last weekend, had they failed to win all of their first five home games of a campaign.

What renders Inter's form more curious is that they have been perfect away from home, beating Hajduk Split, Vaslui, Pescara and Torino without conceding a single goal. But if there has been any temptation to blame the San Siro pitch for his team's travails then Andrea Stramaccioni has done well to resist it. On Sunday he stuck to the line that his team had played well and that the scoreline did not reflect the performance.

Stramaccioni finds himself in an unusual position of strength for a manager at Inter – able to go through such growing pains without immediate fears over his position. The club's owner, Massimo Moratti, is personally invested in this appointment – having stuck his neck out to award the role to a youth team manager with no previous experience at the senior level. For once he had allowed himself to be won over by charisma and energy rather than profile and reputation.

The owner visited the dressing room after Sunday's game, yet did not chastise his manager; instead offering words of consolation and an embrace. That Stramaccioni has his favour was demonstrated in their post-game comments. The manager mooted an eventual move to a three-man defence: a tactical move which doomed Gian Piero Gasperini's tenure from the start last season, yet which this time found the owner's support. "This is different, he is talking about an evolution," insisted Moratti when the point was raised.

Stramaccioni has not been afraid to make bold moves up to this point – indeed, Sunday's game was noteworthy for the fact it was the first time since September 2008 that Javier Zanetti was left out of Inter's starting XI purely as a tactical decision. But that too might be a criticism, the manager's failure to settle on a first-choice XI and style of play reflected in his team's lack of fluidity in their movements.

Either way, he can be grateful that his problems are not yet as significant as those facing his Milan counterpart Massimiliano Allegri. The Rossoneri have failed not only to win, but to score, in any of their home matches so far. This weekend, they proved that they could disappoint away from home as well, beaten 2-1 by an Udinese team who, like Siena, had been without a win.

Many had suggested that this match could be decisive for Allegri's future, claims that only gained momentum after a midweek exchange with Filippo Inzaghi. The manager had run into the former striker – now in charge of Milan's Under-17s – during a visit to the youth team's training facility, and become engaged in a brief but strident "exchange of views".

Initial reports had the pair needing to be separated in order to prevent a physical confrontation, though the club and all parties present were quick to deny the claims. Nevertheless, there was something deeply uneasy about their public reconciliation on the Milan Channel soon afterwards. Inzaghi has already been mooted as a possible successor to Allegri, and there is no love lost between the two following the manager's decision to leave the forward out of his Champions League squad last season.

In any case, the team's vice-president, Adriano Galliani, was quick to clarify on Sunday evening that Allegri's position is not in immediate jeopardy. "We go forward with this manager," said Galliani. "He has the total faith of the president [Silvio Berlusconi] and myself … Now we await our first win of the season on Wednesday."

He was referring to the team's fixture with Cagliari – an opponent that Milan have beaten in each of their last eight meetings at San Siro. On paper, a great opportunity to lift any curse associated with the new pitch. Then again, so were the last eight home games that the two Milanese clubs have shared between them.

Talking points

• Where else to start but the match that wasn't played in Cagliari – authorities deciding on Sunday morning that the home team's game against Roma that afternoon could not go ahead. The match had been slated to be played behind closed doors at the Stadio Is Arena after the venue was once again deemed unsafe to host supporters despite ongoing renovation work designed to bring it up to standard.

Cagliari's owner, Massimo Cellino, disagreed, publishing a statement on the club's website inviting fans and ticket holders to come down anyway – "in a civil and orderly manner" – since the club's engineers had ruled the stadium safe for use.

With the potential for huge public disorder mounting, authorities took what they felt to be the only sensible decision in having the game postponed. With the Italian Football Federation now promising an investigation, and Roma making the case that they and their fans have suffered substantial loss as a consequence of events entirely of their opponents' making, there is every chance that the game will eventually be awarded as a 3-0 win to Roma.

• This was a great week for Fabio Quagliarella, who followed up his goal against Chelsea in the Champions League with two more to lift Juventus past Chievo. Typically for the player, the first – an overhead kick – was also an absolute peach. In a week when Napoli and Lazio both dropped their first points of the season, this was an important statement of intent for Juve – all the more impressive for the fact they had made five changes to the team that drew with Chelsea. Tuesday brings another significant challenge, however, away to old rivals Fiorentina.

• Sampdoria also dropped their first points of the season, outplaying Torino for much of the game at the Marassi but unable to find a way past Jean-François Gillet until an 84th-minute Nicola Pozzi penalty, by which point they had fallen behind to a spot-kick at the other end. Still, level with Lazio in third place after four games, despite starting the season with a one-point deduction, it's safe to say nobody expected quite this start from the Blucerchiati.